This is more of an updated "deskTOP" enclosure that can sit on top of any desk?
It is definitely in your best interest to support at a minimum ATX boards IMHO. "E-ATX gaming" size boards (1" more in dimension) would be my preference personally. I wouldn't worry about XL-ATX or bigger since those aren't popular.
If you can get this made for under $300 or closer to $200 like the NCASE then I think you may be in good shape. Aluminum is expensive so I am not sure how realistic that is.